A salivary vasodilator in the blood‐sucking bug, Rhodnius prolixus

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Abstract
Salivary gland homogenates of the blood‐sucking bug, Rhodnius prolixus induced transient, dose‐dependent relaxation of rabbit aortic preparations pre‐constricted with 200 ng ml−1 noradrenaline, 1 μg ml−1 histamine or 20 ng ml−1 angiotensin II. Such relaxations were less marked when the aorta was constricted by 60 mm KCl. These effects were observed with as little as 0.2 μg ml−1 of crude salivary gland protein. The vasodilator effect was endothelium‐independent, abolished by 50 μm hydroquinone or 50 μm methylene blue, and potentiated by 30 u ml−1 superoxide dismutase. Salivary homogenates generated a coloured compound when reacted with sulfanilic acid in the presence of N‐(1‐naphtyl)‐ethylediamine, indicating the presence of reactive nitrogen groups, equivalent to 35 ± 3 ng of sodium nitrite per pair of glands. Molecular sieving high performance liquid chromatography of salivary gland homogenates generated a single peak of vasorelaxant activity which coincided with the presence of platelet antiaggregating and spasmolytic (guinea‐pig ileum contracted with histamine) activities, as well as with reactive nitrogen groups. It is concluded that a protein of molecular weight 16,500 daltons in the salivary glands of R. prolixus contains reactive nitrogen groups which assist the bug during a blood meal. It is suggested that saliva of blood sucking arthropods is a natural resource of novel pharmacological activities.